(1) Field of the Invention
The present invention relates to crystallized glass or glass ceramics, and, in particular, to biocompatible glass ceramics which are useful for artificial dental roots, artificial tooth crowns and others.
(2) Description of the Prior Art
It is needless to say that the biocompatible materials useful, for example, for tooth replacement materials, are required not to be harmful for living bodies such as human bodies and animal bodies. Among the other various requirements for those biocompatible materials, a high mechanical strength and an excellent biological affinity are also important.
Although alumina and sintered apatite are well known as typical and conventional biocompatible materials in the prior art, they have disadvantages. Alumina cannot be chemically bonded to bones and teeth of the living body, and therefore, any means is required to fixedly connect alumina to the living body. Sintered apatite has not a sufficient mechanical strength as replacements of the bones and the teeth.
In order to reduce the above-described disadvantages of alumina and sintered apatite, glass ceramics are used for biocompatible materials in the prior art. U.S. Pat. No. 3,922,155 by Broemer assigned to Ernst Leitz G.m.b.H. discloses a Na.sub.2 O--K.sub.2 O --MgO--CaO--SiO.sub.2 --P.sub.2 O.sub.3 glass ceramic as a bone replacement material. The glass ceramic includes apatite crystals and has a good biological affinity. However, since the glass ceramic contains Na.sub.2 O and K.sub.2 O, it is insufficient in the mechanical strength and has a low chemical resistance so that it is not maintained stable in the living body for a long time.
Also, MgO--CaO--SiO.sub.2 --P.sub.2 O.sub.5 glass ceramics are disclosed for biocompatible materials in U.S. Pat. No. 4,560,666 by Yoshida et al assigned to Hoya Corporation and Japanese patent application laid open with No. 191252/'82. The glass ceramics contain SiO.sub.2 which is restricted to 41 wt % or less in amount so as to increase apatite crystals dispersed therein, so that the glass ceramics are excellent in chemical bonding with bone. However, the glass ceramics are insufficient in the mechanical strength.
Japanese patent application laid open with No. 158841/'86 discloses another glass ceramic useful for a bone replacement material. The glass ceramic is a porous CaO--P.sub.2 O.sub.5 --SiO.sub.2 glass ceramic having apatite crystals and diopside and/or wollastonite crystals. The glass ceramic is also insufficient in the mechanical strength.